Rename module string to string-h. * modules/string-h: Renamed from modules/string. * modules/string-h-tests: Renamed from modules/string-tests. * modules/string-h-c++-tests: Renamed from modules/string-c++-tests. * tests/test-string-h.c: Renamed from tests/test-string.c. * tests/test-string-h-c++.cc: Renamed from tests/test-string-c++.cc. * tests/test-string-h-c++2.cc: Renamed from tests/test-string-c++2.cc. * doc/posix-headers/string.texi: Update. * doc/posix-functions/strcat.texi: Update. * doc/posix-functions/strcpy.texi: Update. * doc/posix-functions/strncpy.texi: Update. * modules/* (Depends-on): Update. * modules/string: New file.